The main difference is that treatment in tropical fish is nearly impossible; this can often depend greatly on the type and location of the mass. Not only are they difficult to handle so that a human can have clear visual access to them, but some cures such as surgery are basically out of the question. Tumors will generally show themselves as a lump under or on the skin of a fish.
These are a distinct bump or lump, as opposed to the white fluff of skin diseases. For the most part, tumors are benign, although it's very possible for one to grow to a size which makes the fish's quality of life decline and you may have to euthanize it. One type of tumor that does have some success with treatment is the kind that forms under the skin of the gill, causing it to remain open. The cause of this can normally be attributed to a thyroid malfunction .
An article we read suggested this as a possible treatment. Remove the fish to a small solitary tank, and add 1 milligram of potassium iodine for every gallon of water. Improvement can be slow, and the full course of treatment can take up to one month. Internal tumors can be very advanced before the fish shows any signs, such as a swelling of the abdomen. These cases are inevitably fatal, with the rapid growth causing the fish to lose its ability to swim and or eat, at which time you should consider euthanasia.
